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Monday, November 11, 2013

Was the Swamp Ape Bipedal?

by Marcel F. Williams

Tuscany is renowned for its beautiful cities of Florence and Siena, and is historically famous as the birthplace of the Italian Renaissance. But amongst the paleontological community, Tuscany is also known as the birthplace of an extinct Late Miocene ape-- that some paleontologist controversially believe may have been the earliest primate to walk predominantly on just two legs-- and possibly the earliest bipedal ancestor of humankind.

Oreopithecus bambolii first emerged on an ancient island bioprovince known as Tuscany-Sardinia (Tusco-Sardinia) sometime after 9 million years ago where it existed as the sole primate on the island until approximately 7 million years ago. Tuscany-Sardinia was isolated from the rest of the Italian peninsula and from the rest of continental Europe by the marine waters of the Late Miocene Mediterranean.

Skull of Oreopithecus bambolii

Between 11 to 9 million years ago, sea levels fell during a glacial period caused by the deposition of ice and snow on polar land masses. The lower sea levels allowed various mammals from North Africa and Southern Europe to enter the Tuscany region. Small mammals from Europe apparently entered the isolated island region through rafting or swimming. But fauna from North Africa appears to have entered the region via ephemeral land bridges.

The mostly likely ancestor of Oreopithecus was a small African ape know as Mabokopithecus which appears in the fossil record in Africa about 15 million years ago. Oreopithecus and Mabokopithecus were both folivores (planet eaters) that shared a unique dental attribute in their upper molars: a well-defined hypocone-metaconule crest on the upper molars-- a unique characteristic that has never been found in any other monkey or ape living or extinct.

Because its fossil remains are strongly associated with the wetland freshwater environments that existed on Tuscany-Sardinia at that time, Oreopithecus is frequently referred to as the 'swamp ape'. Dryer areas did exist on the island, but Oreopithecus was rare in those deposits while being abundantly represented in the swampy wetland coastal environments on the island.

It is interesting that the African oreopithecine ancestor, Mabokopithecus, existed in an ecological niche largely restricted to riparian woodland areas. This is a niche similar to that of the extant folivorous primate Colobus guereza (the Colobus monkey). Although the Colobus monkey is highly arboreal, it is known to come down from the trees in order to feed on aquatic plants in nearby swamps.

Oreopithecus bambolii has long been at the center of controversy principally because of its remarkable cranio-dental and post cranial similarity to African hominins (human ancestors) which was first fully noted by Johannes Hurzeler as far back as the 1950s. Further adding to the controversy is the argument that Oreopithecus may have also been the earliest obligatory bipedal primate and the first ape to walk exclusively on just two legs.

Oreopithecine remains display a significant number of post cranial characteristics that could be associated with either arboreal or bipedal locomotion. However, there is one post cranial characteristic that is clearly related to bipedality and that's lumbar lordosis, a curvature of the spine that is unique to the hominins (humans and their bipedal ancestors). However, a recent paper by Russo and Shapiro has question the existence of lumbar lordosis in Oreopithecus, arguing that the supposed features may be simply be an artifact of the skeleton's distortion caused by its compression during fossilization. Russo and Shapiro also argue that the arboreal three toed sloth (Bradypus) would be a better convergent model for the skeletal anatomy and locomotive behavior of the extinct oreopithecines rather than the bipedal hominins.

Three-toed sloth (Bradypus)

While slow climbing suspensory behavior has long been argued as an explanation for some of the anatomical attributes of Oreopithecus, such locomotive behavior appears to be contradicted by the exceptionally robust metatarsals of the oreopithecine foot along with the proportions of the foot's entocuneiform which was proximally-distally short and dorso-ventrally high. The length-height index of the oreopithecine entocuneiform related to the mass placed on the hind limbs and is most similar to that of the gorilla. The gorilla's low entocuneiform length-height index is related to the large amount of mass placed on the hind limbs due to its large body size. Oreopithecus, however, was a very small ape, with males typically weighing about 32 kilograms and females approximately half that size. The average Gorilla male weighs 175 kg with average female gorillas weighing about 85 kilograms. So in order to explain, the gorilla-like entocuneiform index, in Oreopithecus, the swamp ape must have been carrying its entire body weight on just its hind limbs. Kohler and Moya- Sola also noted that the power armload arm ratio strongly suggest that Oreopithecus carried its entire body weight on its hind limbs.

There's also strong evidence in the oreopithecine feet of a significantly reduced arboreal ability. The Oreopithecus foot had robust metatarsals plus a non helical ankle joint, characteristics typically associated with terrestrial catarrhines. Kohler and Moya-Sola have also noted that the mobility and grasping ability of the oreopithecine foot had been appreciably reduced relative to arboreal primates and even more so than in terrestrial baboons.

It would also be difficult to understand why Oreopithecus would expend the energy and the risk of being a highly arboreal tree living primate on an island where there were no terrestrial predators. But even on the ground, why would Oreopithecus abandon terrestrial quadrupedalism for bipedalism? The answer may come from its food source.

Chimpanzee wading bipedally with a stick

Orangutan wading bipedally

Gorilla wading bipedally

The coastal wetlands that Oreopithecus preferred were rich in aquatic plants. Harrison and Rook have suggested that Oreopithecus may have specialized in feeding on aquatic plants which were abundant in the wetland coastal areas of the island such as: sedges, water lilies, reeds, cattail, pond- weeds, horestails, and stoneworts which were abundantly represented in the fossil pollen spectrum.

Extant primates that feed on aquatic plants, usually wade bipedally in the shallow waters to access the food resource. Bipedal wading in primates has been observed in: baboons, macaques, the gorilla, orangutan, and in the chimpanzee. Such aquatic bipedalism in order to access aquatic plants comprises as much as 27% of the feeding behavior of the Western Gorilla.

Additionally, freshwater mollusk and turtles were also abundant in the wetland areas of Tuscany-Sardinia island-- along with predatory crocodiles. Turtle and crocodile eggs may have served as a good source of protein for Oreopithecus.

Marine biologist, Alister Hardy, hypothesized that the power precision grip in humans originally evolved as an adaptation for picking up benthic invertebrates. Wading bipedally in shallow water for food resources such as shellfish
and aquatic plants is, of course, common behavior in many
hunter-gatherer human populations. But such behavior has also been observed in non-human primates such as baboons, macaques, guenons, and capuchin monkeys.

Curiously, Oreopithecus also had a hominin-like power precision grip. Such manual dexterity could have evolved in Oreopithecus as a feeding adaptation for picking up the shelled invertebrates that existed in the wetland areas of Tuscany-Sardinia while it was also feeding on aquatic plants.

As the sole primate on the ancient island of Tuscany-Sardinia for nearly two million years, it seems unlikely that Oreopithecus would have avoided the exploitation of freshwater aquatic food resources that were so rich in carbohydrates and proteins.

Sea levels in the Mediterranean began to fall sometime after 7.4 million years ago and the island's isolation from Europe and Africa appears to have ended sometime between 6.9 to 7.2 million years ago. By 6.1 million years ago, global sea levels fell to such an extent that the Mediterranean Sea became completely isolated from in the inflow of marine waters from the Atlantic Ocean. During this period of lowering sea levels, land bridges were created between Europe and North Africa.

The earliest African hominin, Sahelanthropus, appeared in the fossil record in North Africa sometime between 6.8 and 7.2 million years ago. While not much is known about the postcranial remains of Sahelanthropus, its craniodental morphology isremarkably similarto that of Oreopithecus bambolii.

The earliest hominins appear to have radiated into Africa from Southern Europe at the beginning of the Messinian (just before 7 million years ago).

The baboon C retrovirus that heavily infected all African primates, except for Homo, didn't occur until after the baboon and gelada diverged from each other which was sometime after 5 million years ago. The retrovirus also had to occur before the emergence of Homo (2.6 million years ago).

But the australopithecines should have been fully exposed to the baboon retrovirus sometime between that time range.

I argue that the ancestors of Homo were geographically isolated from the rest of Africa during the Pliocene, probably on an island in the Northern Afar region which was flooded by marine waters during the early Pliocene.

But this period of geographic isolation would have ended when sea levels began to lower dramatically at the beginning of the Pleistocene (~2.6 million years ago).

The presence of (high protein) Hydrocharis today in Tuscan marshes plausibly indicates the main aquatic food of Oreo., as it is for the Congo lowland gorilla, who rake it with their fingers while partly submerged (~97% Hydrocharis, ~3% sedges). =History and traditionsAs weIl as the richness of its landscape and nature, the Marshes have maintained the fascination of the historical events related to the great Medici and Lorena families. Here still remain important testimonies of the work of man, which over the centuries have shaped and changed the very structure of the wetland: the canals and port systems, signs of ancient and important waterways; the Medicean Bridge at Cappiano, the centre for controlling the water regime and fishing activities, as well as an important stop along the Via Francigena; the Capannone Farm complex, which was one of the main berthings of the Valdinievole; the buildings of industrial archaeology like the tobacco dryhouses. The commemorative plaques so often found on the cabins or along the banks tell a more recent story: the tragedy of the barbaric massacre committed by the Germans on 23rd August, 1944. A few skilful craftsmen still carry on residual activities related to the marsh grasses in the marshes: gathering and weaving "sarello" (tufted sedge) and "sala" reed-mace (False bulrush) (to wicker seats and cover wine flasks), "Gaggia" (False Indigo) and other typical wetland plants.

Flora Situated on the boundary between the Mediterranean and Continental climates of the Peninsular, the Marshes simultaneously shelter plants adapted to different climates; for example in the Ramone Marshlet, on the edges of the Chiusi Woods, still survive the Frogbit (Hydrocharis morsus-ranae) and the Royal Fern (Osmunda regalis), both plants from a warm wet climate, alongside certain mosses (Sphagnum sp.), more adapted to cold climates of the north and which descended as far as the Marshes during the last Ice Age. Only in the Marshlet, and in a few other areas of the Marsh basin, can still be found fair extensions of the Tufted Sedge (Carex elata), locally called "sarello"; this plant of northern origin develops in bushy formations of more than one individual. Where the immense reed thickets leave space to the free waters, are the "laminas" formed of plants with floating leaves (e.g. the large White and Yellow Water-lilies) which offer one of the last refuges for several highly specialised species: the Southern Bladderwort (Utricularia australis), a floating carnivorous plant, the Fringed Water-lily (Nymphoides peltata), with its beautiful yellow flowers, and the strange, tiny floating fern Salvinia natans, now extremely rare in Tuscany.

"The knowledge that we have now is but a fraction of the knowledge we must get, whether for peaceful use or for national defense. We must depend on intensive research to acquire the further knowledge we need ... These are truths that every scientist knows. They are truths that the American people need to understand." (Harry S. Truman 1948).